Should gay men be screened for anal cancer?

Cases of anal cancer among gay men who are HIV positive have been on the rise since the advent of antiretroviral treatment for those living with the virus.

Consequently questions are now being asked about whether men who have sex with men should be routinely screened for anal cancer using anal cytology (taking cell samples from the area) and high resolution anoscopy (a tube used to see the lining of the anus).

In an article published in Wolters Kluwer Health journal Dr Paul Fox examines the current evidence and opinion on routine anal cancer screening. Dr Fox is a Consultant Physician at the Chelsea and Westminster Hospital and at Freedomhealth Clinic London where he runs a state of the art High Resolution Anoscopy clinic.

Current UK guidelines do not recommend routine anal cancer screening and guidelines from outside the UK vary. For example in New York routine anal cytology is recommend for gay men, whereas leading groups in other states including Texas and California say that there is not yet enough research to form any guidelines.

There are a number of reasons why routine anal screening programmes have not been rolled out. The cost, both of setting up and maintaining the programme, is just one of the factors. Balancing the need for screening with any patient anxiety is another factor as well as concerns over the efficacy of screening.

The sensitivity of anal cytology is regarded as poor and so is used in conjunction with high resolution anoscopy, where medical professionals will look for the precursor lesion to anal cancer known as a high grade squamos intraepithelial lesion (HSIL).

A number of studies have been carried out to try and assess how great the risk of anal cancer is to gay men in a bid to identify groups that could benefit from routine anal cancer screening.

Dr Fox makes some criticism of the small number of studies for the way in which patients were recruited; many were not randomly selected meaning there was a potential selection bias.

However Dr Fox highlighted two recent studies which he was sure eliminated selection bias, one by randomly selecting patients and another by using the entire population of an HIV clinic.

The first study screened the 516 patients of an HIV clinic in Paris. It was found that 473 had HSIL, and that men who had sex with men were more than twice as likely to have HPV lesions - which can be potentially cancerous - than heterosexual men or women.

A second study looked at HIV patients on antiretroviral treatment from different demographic groups, evenly divided between MSM, heterosexual men and women. It found what Dr Fox described as “surprisingly little difference” between the groups in terms of the number of patients with HSIL. Around 5% of people in each group had an HSIL – the anal cancer precursor lesion.

The figure matched data from the days before antiretrovirals were available, leading Dr Fox to conclude that there was a possibility that the rising incidence of anal cancer in HIV-positive patients treated with anti-retroviral therapy is due to patients living longer, which gives greater rise to the cancers occurring.

Dr Fox also concluded that patients on antiretroviral treatment must therefore be at greater risk of their HSIL making a malignant transformation into anal cancer.

There were also concerns that treatment was less effective for HIV patients compared to HIV negative people. Dr Fox looked at a number of studies carried out on the treatment of HSIL and anal cancer.

A study by Goldstone et al showed that 65% of HIV positive men who received infrared coagulation treatment treatment for HSIL had new or persistent lesions after a 10 month follow-up, compared to 50% of patients who were HIV negative. A further study, which differed in its methodology by performing a repeat biopsy of the treatment site at 6 months post-treatment found only 10% of HIV positive patients were disease free.

A study on the outcome of two different types of treatment for HIV positive men with HSIL has provisionally shown little difference. It looked at patients who were given a single infrared coagulation treatment and those who applied trichloroacetic acid once monthly for four months. There was an individual clearance of 68% with individual lesions with IRC and 87% in the group treated with trichloroacetic acid.

A further study involved a placebo controlled study of 53 HIV patients using a self-applied imiquimod cream. In the patients using the cream the response rate was 39% compared to those using the placebo cream.

In a further study where participants were offered open-label imiquimod the response rate was 40% with half of those patients having a complete and sustained resolution of their lesions.

It was noted that the benefit of these treatments is that the lesions disappear and although some recur in different locations it is thought that lesions that have not been static for some years will carry only a low risk of malignant transformation.
According to the article it is therefore reasonable to suppose that treatment of HSIL will reduce the likelihood of anal cancer, but this has not yet been proven.

Dr Fox also concluded that anal cytology is a validated means of detecting anal cancer but is best restricted to selected patients.

He recommends that clinics carry out physical, digital examination of the anus to look for abnormalities and that this becomes the standard at HIV clinics.

A study in San Francisco highlights the important of digital examination. The cases of 21 patients who had developed anal cancer were examined and it was found that 19 had presented with palpable mass, an induration or ulcer. The implication was that physical examination could have picked up these lesions at an early stage.

Patients should also be encouraged to self-examine with Dr Fox saying it may be “just as effective as a cytology based approach”.

He says the clinics must play an important role in encouraging patients to self-examine and helping them learn how to carry it out properly. The report suggests clinicians carry out the initial examination to prevent patients becoming concerned by lumps that are either benign or part of their normal anatomy.

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